The present invention relates to medical devices, and more particularly, to an improved programmable infusion pump for delivering intravenous drugs at a controlled rate to a patient.
It is often necessary to intravenously supply patients with pharmaceutically active liquids over a long period of time at a controlled rate. It is desirable that this be accomplished while the patient is in an ambulatory state.
The prior art includes devices that employ a bag filled with fluid medication that feeds by gravity through IV tubing having drip or other controllers. It is difficult for a patient to be ambulatory with a gravity fed infusion device. In addition, flow control in this type of device is very limited.
Another prior art infusion apparatus comprises an elastic bladder forming a liquid container, an elongated cylindrical housing enclosing the bladder, a flow control valve, and tubing for supply of the liquid to the patient. The elastic walls of the bladder expand along the walls of the cylindrical housing when filled with the liquid, and provide the pressure for expelling the liquid. The bladder is typically filled by hand with a syringe which often requires an inordinate amount of force. Another drawback is that the bladder is forced to expand into an unnatural elongated configuration along the housing walls as it is filled. As a result of this unnatural configuration, the pressure of the bladder varies widely with the volume of liquid therein. Therefore, in most cases, this type of elastic infusion apparatus does not have a reasonably stable pressure and flow rate over the infusion period. Most of such devices either have a flow rate that decreases with pressure, which decreases with volume, or one that remains roughly constant until the end where it surges. Attempts have been made to control pressure and flow rates by means of complicated and expensive flow control valves and devices. Other approaches have utilized exotic and expensive elastic materials in an effort to control the pressures and flow rates.
Another type of infusion apparatus uses pressurized gas as the driving force for the intravenous liquid. In such systems there may be hydraulic feedback through the pneumatic source in order to precisely regulate hydraulic pressure. See for example U.S. Pat. Nos. 4,430,078 of Sprague, 4,335,835 of Beigler et al., and 4,327,724 of Birk et al. Such pneumatically driven infusion devices tend to have reducing flow rates and pressures as the stored pressurized gas source is exhausted.
Still another type of infusion apparatus employs a peristaltic or other positive displacement pump which is electrically driven. Programmable infusion pumps have been provided having the capability for precise tailoring of the fluid delivery rate parameters in different modes, such as, continuous, intermittent, PCA (patient controlled analgesic) and TPN (total parenteral nutrition). Originally, such programmable infusion pumps were large and not well suited for ambulatory patients. They used complex and expensive replacement pump cartridges to maintain sterility.
More recently, small programmable infusion pumps have been available with disposable plastic cartridges that engage a peristaltic pump. However, such cartridges have been bulky and expensive and have required excessive drive power in the pumps, leading to rapid battery drain. Another drawback of these existing programmable infusion systems of this type is that they are complicated and very expensive to manufacture and to maintain.
There is an ever increasing desire in the health care field to get patients out of expensive hospital care environments and back to their homes. Many such patients require intravenously administered medications, but are unable to program existing programmable infusion systems themselves, and trained operators cannot economically visit their homes. In addition, many such patients are unable to change the delivery rates in accordance with subsequent physician prescriptions. Furthermore, they cannot effectively verify the prescribed delivery parameters.
Accordingly, it would be desirable to provide an improved low cost single channel programmable infusion system for delivering intravenous drugs at a controlled rate to an ambulatory patient that can be more easily programmed by a patient, and which will allow patient verification of the prescribed delivery parameters.